1. Field of the Invention
The present invention relates to a large EL panel formed by a plurality of EL display devices, such as organic EL panels, which are arranged in a matrix pattern, and also relates to a manufacturing method for the large EL panel.
2. Description of the Related Art
Small EL flat panels (EL display devices) driven by polysilicon TFTs are usually laminated on a hard and transparent substrate by an adhesive, etc., in order to maintain the flatness thereof. Each of the TFTs control the driving of one of multiple pixels in the EL display devices, so that plane images are displayed.
The EL display devices are described above are typically two to six inches in length measured in a diagonal direction, and provided excellent functions as small image displays.
Conventionally, in theaters and stadiums, large screens, which are capable of displaying clear images, are commonly used in place of electrical scoreboards. In such large screens, a plurality of light sources, such as the above-described EL display devices, light bulbs are arranged in a matrix pattern. Each of the light sources functions as a pixel for forming an image.
In such theaters and stadiums, there is a sufficient distance between the screen and the audience; therefore, the EL display devices having a diagonal length of, for example, several inches should not be a problem.
Recently, on the other hand, instead of CRTs, liquid crystal display panels have been commonly used as displays for televisions and personal computers. In addition, there has been a demand to increase the sizes of the liquid crystal display panels.
In a liquid crystal display, an additional light source is required as a backlight. Thus, to increase the size of the liquid crystal display, the size of the backlight must also be increased. The present situation, however, is such that when a large (50 to 100 inches in diagonal length) and thin display is required, an amount of heat, which increases along with the size of the backlight, will be too large. In addition, the thickness of the display cannot be made thin enough to satisfy the requirement.
Accordingly, the use of the EL display devices driven by TFTs, which will be referred to as TFT-EL display devices in the following disclosure, has been considered. In the TFT-EL display devices, the backlights are not required. In addition, due to the use of the TFTs, the number of pixels may be increased, and response rate become higher, so that high-resolution images may be displayed.
Large TFT-EL display devices, however, have not been realized. Accordingly, to form a large display panel which is 20 to 100 inches in diagonal length, small TFT-EL display devices, which are several inches in diagonal length, must be arranged in a matrix pattern.
Generally, a TFT-EL display device is laminated on a flat-type transparent substrate. Accordingly, TFT-EL display devices cannot be arranged in proximity to each other beyond the peripheries of the transparent substrates.
In addition, a TFT array includes not only a pixel section but also a circuit (driver) section for individually controlling the light emission at the pixels. The circuit section is disposed at a region outside of an image forming area, and prevents the adjacent EL display devices from being arranged in close proximity to each other.
In consideration of the above-described structures and their limitations, an object of the present invention is to provide a large EL display panel and a manufacturing method thereof, in which a plurality of EL display devices are arranged in a matrix pattern, and in which a pitch between the pixels in the pixel section of the TFT array is maintained constant.
The present invention provides a large EL panel including a plurality of EL display devices which are arranged in a matrix pattern on a main transparent substrate which is capable of supporting multiple EL display devices. Each of the EL display devices includes: a base layer over which a luminescent material is applied; an electrode layer which is laminated on one side of the base layer; and a TFT layer. The TFT layer includes a circuit section in which light emission of the luminescent material is controlled by applying a predetermined voltage between the electrode layer and the TFT layer and a pixel section which is superimposed over the other side of the base layer and which is provided with a plurality of pixels which divide the base layer into sections so that light emission of the luminescent material in each section is individually controlled by generating a potential difference between the electrode layer and the TFT layer at the corresponding section. The circuit section of the TFT layer, which is disposed at the region outside a light emitting area, is disposed behind the adjacent EL display device so that light emitting areas of the adjacent EL display devices are arranged in proximity to each other and separated by a predetermined gap.
In addition, the present invention also provides a manufacturing method for a large EL panel in which a plurality of EL display panels are used, each of the EL display panels being constructed of the above-described EL display device and a sub-transparent substrate that supports the EL display device. The manufacturing method for the large EL display panel includes the steps of: removing the EL display devices from the sub-transparent substrates; arranging the obtained EL display devices on a main transparent substrate, which is broader than the sub-transparent substrate, in a matrix pattern and in a manner such that light emitting areas of the adjacent EL display devices are in proximity to each other; and disposing and fixing the circuit section of the TFT layer, which is disposed at the region outside the light emitting area, behind the adjacent EL display device.
In the case in which a large display panel is formed by using the EL display devices, a problem has occurred that sub-transparent substrates, which are larger than the EL display devices, prevent the EL display devices from being arranged in proximity to each other. Accordingly, by applying, for example, separation and transfer techniques described in Japanese Unexamined Patent Application Publication Nos. 10-125930 and 10-125931, it is possible to arrange the EL display devices in proximity to each other.
With the above-described techniques, the EL display devices may be separated from the sub-transparent substrates by applying a mechanical or chemical force to adhesive layers which are disposed therebetween, and may be transferred to another substrate.
Each of the TFT layers has a pixel section and a circuit section. The pixel section is superimposed over the light emitting area, so that no problems occur. In contrast, however, the circuit section is disposed at the periphery, usually at two sides, of the TFT layer, and at the region outside the light emitting area. Accordingly, the circuit section prevents the adjacent EL display devices from being arranged in proximity to each other, so that the ability of the TFTs to display high-resolution images cannot be sufficiently exploited. According to the present invention, however, the circuit section is disposed behind the adjacent EL display device, so that a high resolution and large EL display panel may be constructed.
The manufacturing process of the large EL display panel will be described below. First, the EL display devices are removed from the sub-transparent substrates by using the above-described separation and transfer technique. Then, the EL display devices are arranged on a main transparent substrate, which is broader than the sub-transparent substrate, in a matrix pattern in a manner such that the light emitting areas of the adjacent EL display devices are in proximity to each other. Then, the circuit section of the TFT layer, which is disposed at the region outside the light emitting area, is disposed and fixed behind the adjacent EL display devices.
According to the present invention, the EL display devices are several inches in diagonal length, and the main transparent substrate is 20 to 100 inches in diagonal length.
In addition, the predetermined amount of gap between the light emitting areas of the EL display devices is approximately the same as the pitch between pixels provided in the pixel section of the TFT layer.
To dispose the circuit section behind the adjacent EL display device, the TFT layer is bent at the boundary between the pixel section and the circuit section.
Alternatively, a step portion that changes the positions of the adjacent EL display devices in the thickness direction may be provided so as to dispose the circuit section behind the adjacent EL display device.
Alternatively, the adjacent EL display devices may be inverted so as to arrange the base layers of the adjacent EL display devices in the same plane.